In general, an ordinary bicycle comprises portions such as a bicycle frame, a steering handle, a front guide rolling wheel, a rear driving wheel, and a sprocket drive mechanism of pedal power, adapted to be used as a vehicle ridden on smooth and solid road surface and to be prevailingly used for leisure and body building activities.
An ordinary bicycle travels forward in a manner that the front and rear wheels roll forward. During travel the front and rear wheels contact the road surface at one point so that weight of the bicycle and the load thereof and momentum all concentrate at the very small contact area between the wheels and the road surface. When confronted with a loose and soft or wet and slippery road surface on snowfield, grassland, a sandy land or a muddy land, the front and rear wheels of the bicycle are likely to sink into the road or uncontrollably skid, so that scope of use of the bicycle is limited.
In order to allow a user to ride a vehicle similar to an ordinary bicycle on a loose, soft, wet, or slippery road surface such that leisure or body building activities can be extended to snowfield, grassland, a sandy land or a muddy land, there is a need to improve the currently existing designs of front and rear wheels of an ordinary bicycle, for example, by increasing contact area between the rear driving wheel and the road surface, or changing the front guide rolling wheel into a front guide sliding board, so as to enhance the capability of preventing sinking and reducing the out-of-control cases.
The utility model patent CN2628412Y discloses a “multifunctional snowfield sports body-building bicycle”, wherein the front guide rolling wheel of an ordinary bicycle is changed into a sliding board connected to the distal end of the front rod of the bicycle frame by a suspension structure, and the rear wheel is not modified. The utility model is designed to improve the capability of an ordinary bicycle preventing out-of-control skidding when traveling on a snowfield, and does not provide any technical measures to solve the wheel sinking problem when an ordinary bicycle travels on a soft and loose road surface.
Another utility model patent CN2262524Y discloses a “caterpillar bicycle”. Obviously the utility model is targeted at the wheel sinking problem when an ordinary bicycle travels on a soft and loose road surface and put forwards that the rear driving wheel is changed in a manner that two sets of track wheels are arranged side by side and each set of track wheel is formed by three wheels provided with a caterpillar, whereby “the contact area between the wheels and the road surface is greatly increased” and “the frictional force between the wheels and the road surface is greatly increased”. But, just for the reason, this modification deprives the bicycle of being flexibly operated and easily steered.
Therefore, the art of record does not provide a practical and feasible technical solution to the aforesaid problems.